β-Carboline belongs to the group of indole alkaloids and consist of pyridine ring that is fused to an indole skeleton.[2] The structure of β-carboline is similar to that of tryptamine, with the ethylamine chain re-connected to the indole ring via an extra carbon atom, to produce a three-ringed structure. The biosynthesis of β-carbolines is believed to follow this route from analogous tryptamines.[3] Different levels of saturation are possible in the third ring, which is indicated here in the structural formula by colouring the optionally double bonds red and blue:

Eight plant families are known to express 64 different kinds of β-carboline alkaloids. By dry weight, the seeds of Peganum harmala (Syrian Rue) contain between 0.16%[4] and 5.9%[5] β-carboline alkaloids.

As a result of the presence of β-carbolines in the cuticle of scorpions, their skin is known to fluoresce when exposed to certain wavelengths of ultraviolet light such as that produced by a blacklight.[6]